4 Energy for Life Processes Review: All living things use energy - autotrophs / heterotrophsAutotrophs- organisms that manufacture their own food.Most autotrophs use PHOTOSYNTHESIS to obtain food.Besides plants, algae and some bacteria are photosynthetic organisms
8 Overview - What is the general equation for photosynthesis?
9 Tracking atoms in photosynthesis Reactants:6 CO212 H2OProducts:C6H12O66 H2O6 O2Figure 10.4 Tracking atoms through photosynthesisPhotosynthesis is a redox process in whichH2O is oxidized and CO2 is reduced
10 Today’s Focus:Photosynthesis: process of converting solar energy into chemical energyWe can break down photosynthesis into two different stages:Light-dependent reactionsLight-independent reactionsWhat are examples of transformations of energy we encounter every day?Focus question: How do plants convert solar energy into chemical energy?
12 Not all plants photosynthesize: parasitic Dodder
13 Where in plants does photosynthesis occur? All green parts13
14 All green parts of a plant have chloroplasts! Lots of plant cells
15 zoom into a plant cell inside a chloroplast Chloroplast – is a light absorbing organelleFeatures inside:GRANA (granum – singular) - stacks of thylakoids. (thigh)STROMA- solution that surrounds thylakoids“Leaves have about 500,000 chloroplasts per millimeter squared of leaf surface”Green color is due to chlorophyll pigment
17 Stop and JotIn a typical plant cell, what are the different membranes light has to cross to reach chlorophyll?(cell wall, cell membrane, chloroplast membrane, and thylakoid membrane)
18 Beginning of photosynthesis story (Part I the light reactions): Step 1. Light must be absorbed into the chloroplasts.One cell in a plant leaf can have 50 or more chloroplasts.BASICS OF LIGHTSunlight -> white light (really the whole visible spectrum) ROYGBIVWavelengthPigment- compound that absorbs lightAbsorbs, reflects, transmits.Absorption spectra
20 ThylakoidIn membrane - lots of pigments: most imp. pigment -> chlorophyllsAccessory pigments - chlorophyll b, carotenoids, etc.In leaves of plants the chlorophylls are most abundant pigment -> thus leaves green.In Autumn - lose chlorophylls-> other pigments show through.Non-photosynthetic parts of plant?
21 interacts with hydrophobic regions of proteins inside FigCH3in chlorophyll aCHOin chlorophyll bPorphyrin ring:light-absorbing“head” of molecule;note magnesiumatom at centerFigure Structure of chlorophyll molecules in chloroplasts of plantsHydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts; H atoms notshown
24 i Light NADP+ ADP Light Reactions Chloroplast H2O + P Fig. 10-5-1 Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleChloroplast
25 i Light NADP+ ADP Light Reactions ATP NADPH Chloroplast O2 H2O + P FigH2OLightNADP+ADP+PiLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplastO2
26 i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH FigH2OCO2LightNADP+ADP+PiCalvinCycleLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplastO2
27 i CO2 Light NADP+ ADP Calvin Cycle Light Reactions ATP NADPH FigH2OCO2LightNADP+ADP+PiCalvinCycleLightReactionsATPFigure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycleNADPHChloroplast[CH2O](sugar)O2
30 Chlorophyll pigment is found in the thylakoid membrane How does chloroplast structure relate to its function?The stacks of thylakoids help to increase the surface area, allowing for more photosynthesis to occur. Having the thylakoids stacked also helps decrease the volume a chloroplast occupies, allowing numerous chloroplasts to be in a cell and also increase photosynthesis.photosynthetic cells must be intricately set up in order to be able to harvest light energy & not let it dissipate in unproductive ways)
31 (INTERIOR OF THYLAKOID) FigPhotosystemSTROMAPhotonPrimaryelectronacceptorLight-harvestingcomplexesReaction-centercomplexe–Thylakoid membraneFigure How a photosystem harvests lightPigmentmoleculesTransferof energySpecial pair ofchlorophyll amoleculesTHYLAKOID SPACE(INTERIOR OF THYLAKOID)
58 Photorespiration CO2 becomes scarce Rubisco binds to O2 instead of CO2 ATP consumed rather than generated!No sugar produced!Consumes organic material from Calvin Cycle!What’s the point?In some case clear evidence that photorespiration protects plants from damaging products of light reaction which build up when CO2 is scarce